The present invention relates to a device for preventing drying of ink to be used in a writing instrument such as a fountain pen, marking pen, or ball-point pen internally provided with an ink-cartridge containing volatile ink.
Generally, a writing instrument using ink is provided with an ink-cartridge, which contains ink, within the holder and a penpoint at the end thereof.
A writing instrument of this kind has a drawback resulting in total or partial loss of applicability thereof to writing due to evaporation of solvent contained in the ink while kept unused for a long time extending from the time when the instrument is delivered by the maker to that when bought by the user or passing while possessed by the user.
In the case a writing instrument is made of plastic material, however tightly the cap is fitted on the holder thereof, total or partial loss of applicability of the instrument to writing is unavoidable because of the nature of the plastic material permitting permeation of vapor of solvent when the instrument is unused for a long term.
To overcome the above problem, an attempt has been made to reduce dry of the ink in accordance with which a liquid retainer internally impregnated with liquid is held in the case of the writing instrument so that drying of ink is controlled by evaporation of solvent within the case.
However, nothing has been examined about a problem concerning the relationship between vapor pressure of the ink and that of the liquid and by reason that the vapor pressure of the liquid is lower than that of ink, solvent in the ink sometimes evaporates earlier than the liquid in order to maintain equilibrium of vapor pressure of ink and liquid in an air-tight case, and is absorbed by the liquid retainer contrary to the purpose, thereby interrupting the effect of preventing drying of ink.
An object of the present invention is to provide a device capable of preventing drying of ink in a writing instrument for a long period of time.
Another object of the present invention is to provide a device capable of preventing development of opacity in the transparent holsder of the writing instrument so as to permit constant observation of the degree of ink consumption in the ink-cartridge and maintain good appearance of the instrument.